What does admissible heuristic mean?Provide one guideline in designing better admissible heuristics

An admissible heuristic in the context of search algorithms in artificial intelligence is a heuristic function that never overestimates the cost of reaching the goal. In other words, it is optimistic. It always assumes that the cost is less than or equal to the actual cost. This is important in search algorithms because it ensures that the algorithm is "optimistic" and does not prematurely discard potential solutions.

One guideline for designing better admissible heuristics is to use domain knowledge. Domain knowledge refers to any information that can be used to describe the problem space and can help in estimating the cost to reach the goal. For example, in a pathfinding problem, an admissible heuristic could be the straight-line distance (also known as Euclidean distance) from the current position to the goal, as it never overestimates the actual shortest path. This is because, in reality, the path may not be straight due to obstacles, but the straight-line distance will always be less than or equal to the actual path.